Acrylonitrile polymer composition stabilized with metal formaldehyde sulfoxylate, ethylenediamine tetra-acetic acid and sodium salts thereof, and an inorganic acid, and method of making same



United States atent O ACRYLONITRILE POLYMER COMPOSITION STABILIZED WITHMETAL FORMALDE- HYDE SULFOXYLATE, ETHYLENEDIAMINE TETRA-ACETIC ACID ANDSODIUM SALTS THEREOF, AND AN INORGANIC ACID, AND METHOD OF MAKING SAMELloyd T. Jenkins, Decatur, Ala., and Richard R. Holmes,

Bethesda, Md., assignors to The Chernstrand Corporation, Decatur, Ala.,a corporation of Delaware No Drawing. Application May 23, 1956 SerialNo. 586,659

ZO'Claims. (Cl. 260-32.6)

This invention relates to the stabilization of acrylonitrile polymersand blends thereof. More particularly, it relates to the stabilizationof acrylonitrile polymers and blends thereof which have a tendency todevelop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, isintended to include homopolymers, copolymers, and blends thereof, saidpolymers containing at least 80 percent by weight of polymerized orcopolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrileare generally insoluble in the more common solvents. And, in thoseinstances where suitable solvents have been found, in order to effectsolution, the application of heat is usually necessary. Where heat isemployed to effect solutions, from which shaped articles are to beformed, a tan to dark brown color frequently develops in the solutionsand therefore is carried over into the product formed therefrom. Thiscolor also develops in solutions upon standing for prolonged periods oftime. i

The mechanism which causes color formation has not been definitelyascertained, although a variety of reasons therefor have been advanced.The presence of metal ions, such as iron, copper and manganese in thesolutions may cause the color. The employment of amide compounds assolvents may result in formation of amines when heat is applied andcause color in the compositions. Impurities present in the solvents havealso been cited as a cause. Whatever may be the reason for colorformation, it results in compositions and products of undesirablestandards and therefore, has been the source of concern, particularly incommercial operations where such types of polymers or copolymers areemployed.

Accordingly, it is an object of the present invention to preventundesirable color formation in acrylonitrile polymer compositions.

Another object is to minimize color formation when solutions of theacrylonitrile polymers are permitted to stand for a prolonged period oftime or upon application of heat.

It is also an object of the invention to prevent color formation inacrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutionsof acrylonitrile polymers and articles produced therefrom havingimproved color characteristics.

Other objects and advantages will be apparent from a consideration ofthe description of the invention which follows hereafter.

In general, the objects of the invention are accom plished by dissolvingthe polymer of acrylonitrile in a suitable solvent therefor andpreventing or minimizing color formation by the presence in the solutionas an inhibiting agent, a combined reagent comprising an organic metalsulfoxylate, ethylene diamine tetra-acetic 2,878,204 Patented Mar. 17,1959 general formula,

0 i R 0-M in which R is an alkanol group containing 1 to 3 carbon atoms,an acyl group containing 1 to 3 carbon atoms or an aryl group containing6 to 8 carbon atoms, n is an integer from 1 to 2, and M is sodium,potassium, zinc, etc. Compounds illustrative of this class are sodiumformaldehyde sulfoxylate, zinc formaldehyde sulfoxylate, potassiumformaldehyde sulfoxylate, zinc acetaldehyde sulfoxylate, sodiumacetaldehyde sulfoxylate, potassium acetaldehyde sulfoxylate, zincpropionaldehyde sulfoxylate, sodium propionaldehyde sulfoxylate,potassium propionaldehyde sulfoxylate, etc.

The components of the inhibiting agent may be employed in equal orunequal amounts, any one constituent being present in a range of from 98to 1 percent in a three component system. The total amount of inhibitingagent may be employed in a range of about 0.3 to 15 percent, based onthe total polymer Weight. However, it is preferred that the inhibitingagent of the instant invention be present in a small amount compared tothe amount of polymer dissolved. Thus, although the amount is notcritical, it is preferred that the inhibiting agent be present in theamount of about 0.3 to 3.0 percent, based on the total Weight of thepolymer. The inhibiting agent may be added to the solvents before orafter the polymer is dissolved therein. The inhibiting agent permitsexposure to high temperatures for prolonged standing periods without thedevelopment of the objectionable color which usually results in suchsolutions. The compositions of the instant invention may be prepared ina varying temperature range. For example, the compositions of theinstant invention may be prepared by mixing the polymer, a suitablesolvent and the inhibiting agent at any temperature or heating themixture to a temperature up to the boiling point of the solvent.

Among the acids having an ionization constant greater than l 10- whichmay be employed in practising the instant invention are sulfuric acid,nitric acid, phosphoric acid, hydrochloric acid, etc.

Among the solvents which may be used in practising the instant inventionare N,N-dimethylformamide, N,N- dimethylacetamide, aqueous zincchloride, sulfuric acid, aqueous nitric acid, aqueous sodiumthiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in the practice of thepresent invention, are polyacrylonitrile, copolymers, including binaryand ternary polymers containing at least percent by weight ofacrylonitrile in the polymer molecule, or a blend comprisingpolyacrylonitrile or copolymers comprising acrylonitrile with from 2 to50 percent of another polymeric material, the blend having an overallpolymerized acrylonitrile content of at least 80 percent by weight.While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent of acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be understood that theinvention is likewise applicable to polymers containing less than 80percent acrylonitrile and the same stability is realized with theinhibiting agents defined herein. The acrylonitrile polymersconfabrication operations.

taining less than 80 percent acrylonitrile are useful in forming films,coating compositions, molding operations, lacquers, etc., in all ofwhich applications the alleviation of undesirable color is extremelyimportant.

, For example, the polymer may be a copolymer of from 80 to 98 percentacrylonitrile and from 2 to 20 percent of another monomer containing theC=C linkage and copolymerizable with acrylonitrile. Suitablemonoolefinic monomers include acrylic, alpha-chloroacrylic andmethacrylic acids; the acrylates, such as methylmethacrylate,ethylmethacrylate, butylmethacrylate. methoxymethyl methacrylate,beta-chloroethyl methacrylate, and the corresponding esters of acrylicand alphachloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylidene chloride, l-chloro-l-bromoethylene;methacrylonitrile; acrylamide and methacrylamide; alphachloroacrylamide,or monoalkyl substitution products thereof, methyl vinyl ketone; vinylcarboxylates, such as vinyl acetate, vinyl chloroacetate, vinylpropionate, and vinyl stearate; N-vinylimides, such asN-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters;itaconic acid and itaconic ester; N-vinylcarbazole; vinyl furane; alkylvinyl esters; vinyl sulfonic acid; ethylene alpa, beta-dicarboxylicacids or their anhydrides or derivatives, such as diethylcitraconate,diethylmesaconate, styrene, vinyl naphthalene; vinyl-substitutedtertiary heterocyclic amines, such as the vinylpyridines and alkylsubstituted vinylpyridines, for example, 2-vinylpyridine,4-vinylpyridine, Z-methyl-S-vinylpyridine, etc.; l-vinylimidazole andalkyl-substituted l-vinylimidazoles, such as 2-, 4-, orS-methyl-l-vinylimidazole, and other Q C containing polymerizablematerials.

The polymer may be a ternary interpolymer, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespecifically, and preferably, the ternary polymer comprisesacrylonitrile, methacrylonitrile, and 2-vinylpyridine. The ternarypolymers preferably contain from 80 to 97 percent of acrylonitrile, from1 to percent of a vinylpyridine or a l-vinylimidazole, and from 1 to 18percent of another substance, such as methacrylonitrile or vinylchloride.

The polymer may also be a blend of polyacrylonitrile or of a binaryinterpolymer of from 80 to 99 percent acrylonitrile and from 1 to 20percent of at least one other C=C containing substance with from 2 to 50percent of the weight of the blend of a copolymer of from 10 to 70percent of acrylonitrile and from to 90 percent of at least one otherC=C containing polymerizable monomer. Preferably, when the polymericmaterial comprises a blend, it will be a blend of a copolymer of 90 to98 percent acrylonitrile and from 2 to 10 percent of anothermono-olefinic monomer, such as vinyl acetate, which is not receptive todyestulf, with a sufiicient amount of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of avinyl-substituted tertiary heterocyclic amine, such as vinylpyridine orl-vinylimidazole, to give a dyeable blend having an overallvinylsubstituted tertiary heterocyclic amine content of from 2 to 10percent, based on the weight of the blend.

The polymers, useful in the practice of the present invention, may beprepared by any conventional polymerization procedures, such as masspolymerization methods, solution polymerization methods, or aqueousemulsion procedures. However, the preferred practice utilizes suspensionpolymerization Wherein the polymer is prepared in finely divided formfor immediate use in the fiber The preferred suspension polymerizationmay utilize batch procedures, wherein monomers are charged withan-aqueous medium containing the necessary catalyst and dispersingagents. A more desirable method involves the semi-continuous procedurein which the polymerization reactor containing the aqueous medium ischarged with the continuous withdrawal of ployed.

The polymerization is catalyzed by means of any water-soluble peroxycompound, for example the potassium, ammonium and other water-solublesalts of peroxy acids, sodium peroxide, hydrogen peroxide, sodiumperborate, the sodium salts of other peroxy acids, and any otherwater-soluble compound containing a peroxy group (O-O-). A widevariation in the quantity of peroxy compound is possible. For example,from 0.1 to 3.0 percent by Weight of the polymerizable monomer may beused. The catalyst may be charged at the outset of the reaction, or itmay be added continuously or in increments throughout the reaction forthe purpose of maintaining a more uniform concentration of catalyst inthe reaction mass. The latter method is preferred because it tends tomake the resultant polymer more uniform in its chemical and physicalproperties.

Although the uniform distribution of the reactants throughout thereaction mass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of reagents by using inertwetting agents, or emulsion stabilizers. Suitable reagents for thispurpose are the water-soluble salts of fatty acids, such as sodiumoleate and potassium stearate, mixtures of water-soluble fatty acidsalts, such as common soaps prepared by the saponification of animal andvegetable oils, the amino soaps, such as salts of triethanolamine anddodecylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfuric acid and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilicradicals. The quantity of emulsifying agents will depend upon theparticular agents selected, the ratio of monomer to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass orglass-lined vessels which are provided with a means for agitating thecontents. Generally rotary stirring devices are the most effective meansof insuring the intimate contact of the reagents, but other methods maybe successfully employed, for example by rocking or tumbling thereactors. The polymerization equipment generally used is conventional inthe art and the adaptation of a particular type of apparatus to thereaction contemplated is within the province of one skilled in the art.The articles manufactured therefrom may be produced by well-knownconventional methods, for example, the wet-spinning, dry-spinning andmelt-spinning methods for producing fibers.

The following examples are illustrative rather than limitative and allparts, proportions and percentages are by weight unless otherwisespecified.

EXAMPLE I 7.5 grams of a polymer blend of 88 percent of a copolymercontaining 94 percent of acrylonitrile and 6 percent of vinyl acetateand 12 percent of a copolymer of 50 percent of acrylonitrile and 50percent of Z-methyl- S-vinyl pyridine were added to 45 milliliters ofN,N-dimethylacetamide containing approximately 0.05 gram of titaniumdioxide. The mixture was stirred and heated to 70 C. It was then quicklycooled to room temperature and the color measured. This sample was usedas a control. The purity is set forth below. Subsequently, a like samplewas prepared but with 0.225 gram of a color inhibitor containing 0.075gram each of sodium formaldehyde sulfoxylate, ethylene diaminetetra-acetic acid and sulfuric acid. The purity is set forth below.

desired monomers and the polymer may also be em- EXAMPLE II 7.5 grams ofa copolymer containing '94 percent of acrylonitrile and 6 percent ofvinyl acetate were added to 45 milliliters of N,N-dimethylacetamidecontaining approximately 0.05 gram of titanium dioxide. The mixture wasstirred and heated for 35 minutes at 70 C. It was then quickly cooled toroom temperature and the color measured. This sample was used as acontrol. The purity is set forth below. Subsequently, a like sample wasprepared but with 0.225 gram of an inhibiting agent containing 0.075gram each of sodium formaldehyde sulfoxylate, ethylene diaminetetra-acetic acid and sulfuric acid. The purity is set forth below.

Table II Inhibitor Percentage Purity Used Control 10.2 SodiumFormaldehyde Sulfoxylate, Ethylene gizfiriulue Tetra-Acetic Acid andSulfuric 3 4 6 c EXAMPLE III below.

Table III Inhibitor Percentage Purity Used Control 8.5 SodiumFormaldehyde Sulfoxylate, Ethylene gialrinine Tetra-Acetic Acid andSulfuric 3 2 cl The sodium and acid salts of ethylene diaminetetraacetic acid when employed in practising the present invention willgive the same results as ethylene diamine tetra-acetic acidwith respectto the purity readings as set forth above.

The tests for color indicative of approaching whiteness used throughoutthe examples consist of measurements of purity as calculated from thetristimulus values determined on a General Electric spectrophotometer bythe methods recommended by the Standard Observer and Coordinate Systemof the International Commission on Illumination, as fully set forth inthe Handbook of Colorimetry published by The Technology Press,Massachusetts Institute of Technology, in 1936.

The compositions of the instant invention present many advantages. Forexample, products formed from the polymer solutions of the instantinvention are free of objectionable color and therefore of greatercommercial value. In preparing the polymer solutions, heat may beapplied without the danger of color formation and the solutions, ifnecessary, may stand for prolonged periods and remain free of color. Theinhibiting agents are readily available and inexpensive. Therefore, nogreat increase in production cost is necessary. The compositionscontaining the inhibitors may be prepared without going through detailedand elaborate procedures that necessitate expensive changes in thedesign of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparentlywidely different embodiments: of this invention can be made withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims,

We claim:

1. A new composition of matter comprising a polymer containing at leastpercent of acrylonitrile and up to 20 percent of another polymerizablemono-olefinic monomer copolymerizable therewith, a solvent therefor, andan inhibiting agent containing substantially equal proportions by weightof (I) a compound having the general formula 0 R O--M wherein R is aradical selected from the group consisting of alkanol groups containing-1 to 3 carbon atoms, n is an integer from 1 to 2, and M is a metalselected from the group consisting of sodium, potassium and zinc; (II) acompound selected from the group consisting of ethylenediaminetetra-acetic acid and the sodium and acid salts of ethylenediaminetetra-acetic acid; and an inorganic acid having an ionization constantgreater than 1 1-O- 2. A new composition of matter as defined in claim 1wherein the polymer is a copolymer containing from 80 to 98 percent ofacrylonitrile and from 2 to 20 percent of another polymerizablemono-olefinic monomer copolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymeris a blend of 80 to 99 percent of (A) a copolymer containing to 98percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile and 30 to 90 percent of Z-methyl-S-vinyl pyridine.

4. A new composition of matter as defined in claim 1 wherein the polymeris polyacrylonitrile.

5. A new composition of matter as defined in claim 1 wherein compound(I) is sodium formaldehyde sulfoxylate.

\ 6. A new composition of matter as defined in claim 1 wherein compound(I) is potassium formaldehyde sulfoxylate.

7. A new composition of matter as defined in claim 1 wherein compound(I) is Zinc formaldehyde su'lfoxylate.

8. A new composition of matter as defined in claim 1 wherein compound(II) is ethylene diamine tetra-acetic acid.

9. A new composition of matter as defined in claim 1 wherein compound(II) is the sodium salt of ethylene diamine tetra-acetic acid.

10. A new composition of matter as defined in claim 1 wherein compound(II) is the disodium acid salt of ethylene diamine tetra-acetic acid.

11. A new composition of matter as defined in claim 1 wherein thesolvent is N,N-dimethylacetamide.

12. A new composition of matter comprising a polymer blend of (A) acopolymer containing 90 to 98 percent of acrylonitrile and 2 to 10percent of another polymerizable mono-olefinic monomer and (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of a vinyl substituted tertiary heterocyclic amine,

formula wherein R is a radical selected from the group consisting ofalkanol groups containing 1 to 3 carbon atoms, n is an integer from 1 to2, and M is a metal selected from the group consisting of sodium,potassium and zinc; (II) a compound selected from ethylene diaminetetraacetic acid and the sodium and acid salts of ethylene diaminetetra-acetic acid, and an inorganic acid having an ionization constantgreater than 1X 13. A new composition of matter comprising a copolymercontaining 80 to 98 percent of acrylonitrile and 2 to 20 percent ofvinyl acetate, a solvent therefor, and 0.3 to percent, based on thetotal weight of the polymer, of an inhibiting agent, said inhibitingagent containing substantially equal proportions by weight of (I) acompound having the general formula wherein R is a radical selected fromthe group consisting of alkanol groups containing 1 to 3 carbon atoms, nis an integer from 1 to 2, and M is a metal selected from the groupconsisting of sodium, potassium and zinc; (II) a compound selected fromthe group consisting of ethylenediamine tetra-acetic acid and the sodiumand acid salts of ethylenediamine tetra-acetic acid; and sulfuric acid.

14. A new composition of matter comprising a polymer blend of 80 to 99percent of (A) a copolymer containing 90 to 98 percent of acrylonitrileand 2 to 10 percent of vinyl acetate and 1 to percent of (B) a copolymercontaining 10 to 70 percent of acrylonitrile and to 90 percent of2-methyl-S-vinylpyridine, a solvent therefor, and 0.3 to -l5 percent,based on the total Weight of the polymer of an inhibiting agent, saidinhibiting agent containing substantially equal proportions by weight of(I) a compound having the general formula 0 2*? l R OM ]n wherein R is aradical selected from the group consisting of alkanol groups containing1 to 3 carbon atoms, n is an integer from 1 to 2, and M is a metalselected from the group consisting of sodium, potassium and Zinc; (II) acompound selected from the group consisting of ethylenediaminetetra-acetic acid and the sodium and acid salts of ethylenediaminetetra-acetic acid; and sulfuric acid.

15. A new composition of matter comprising polyacrylonitrile, a solventtherefor, and 0.3 to 15 percent based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of (I) a compound having thegeneral formula 0 i R O--M wherein R is a radical selected from thegroup consisting of alkanol groups containing 1 to 3 carbon atoms, n isan integer from 1 to 2, and M is a metal selected from the groupconsisting of sodium, potassium and zinc; (II) a compound selected fromthe group consisting of ethylenediamine tetra-acetic acid and the sodiumand acid salts of ethylenediamine tetra-acetic acid; and sulfuric acid.

16. A method for preparing a new composition of matter comprising mixinga polymer containing at least percent of acrylonitrile and up to 20percent of another polymerizable mono-olefinic monomer copolymerizabletherewith, a solvent therefor, and an inhibiting agent containingsubstantially equal proportions by weight of (I) a compound having thegeneral formula wherein R is a radical selected from the groupconsisting of alkanol groups containing 1 to 3 carbon atoms, n is aninteger from 1 to 2, and M is a metal selected from the group consistingof sodium, potassium and zinc; (II) a compound selected from the groupconsisting of ethylenediamine tetra-acetic acid and the sodium and acidsalts of ethylenediamine tetra-acetic acid; and an inorganic acid havingan ionization content greater than l 10 and heating the mixture to forma homogeneous solution.

-17. The method as defined in claim 16 wherein the polymer is acopolymer containing from '80 to 98 percent of acrylonitrile and from 2to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith.

18. The method as defined in claim 16 wherein the polymer is a blend of80 to 99 percent of (A) a copolymer containing to 98 percent ofacrylonitrile and 2 to 10 percent of vinyl acetate and l to 20 percentof (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30to 90 percent of 2-methyl-5-vinyl pyridine.

19. The method as defined in claim 16 wherein the polymer ispolyacrylonitrile.

20. A method for preparing a new composition of matter comprising mixinga polymer blend of '80 to 99 percent of (A) a copolymer containing 90 to98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and lto 20 percent of (B) a copolymer containing 10 to 70 percentacrylonitrile and 30 to 90 percent of 2-methyl-5 vinylpyridine, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of sodium formaldehydesulfoxylate, ethylenediamine tetra-acetic acid, and sulfuric acid andheating the mixture to a temperature in the range of 25 C. to theboiling point of the mixture to form a homogeneous solution.

References Cited in the file of this patent UNITED STATES PATENTS2,502,030 Scheiderbauer Mar. 28, :1950

2,560,694 Howard July 17, 1951 2,613,194 Craig Oct. 7, 1952 2,648,593Stanton Aug. 11, 1953 FOREIGN PATENTS 1,027,445 France May 12, 1953

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST80 PERCENT OF ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHERPOLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENTTHEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUALPROPORTIONS BY WEIGHT OF (I) A COMPOUND HAVING THE GENERAL FORMULA